1. Field of the Invention
The present invention relates to a method of resin molding and a resin molding machine for the method.
2. Description of Related Art
The applicant of the present invention has invented molding machines, in which parting faces of molding dies are covered with release film while molding (see Japanese Patent Kokai Gazettes No. 8-142105, No. 8-142109 and No. 9-57785). In the conventional resin molding machines, the parting faces, which include cavities, of the molding dies are covered with the release film, then resin molding is executed in the cavities. By using the release film, resin can be solidified without sticking to the molding dies. Further, molded products can be easily ejected from the molding dies, so no ejector pins are required and structures of the molding dies can be simpler. Many types of resin, e.g., tablet, pellet, liquid, can be employed in the conventional molding machines.
FIG. 31 is a front view of a conventional resin molding machine, in which no release film is used; FIG. 32 is a plan view thereof. In the resin molding machine, a part xe2x80x9cAxe2x80x9d is a press section for clamping and molding work pieces, e.g., lead frames, with resin; a part xe2x80x9cBxe2x80x9d is a work feeding section, in which the work pieces are fed; a part xe2x80x9cCxe2x80x9d is a tablet feeding section, in which resin tablets are fed; a part xe2x80x9cDxe2x80x9d is a loading section, in which the work pieces and the resin tablets are arranged and set into a molding die; a part xe2x80x9cExe2x80x9d is an unloading section, in which molded products are taken out from the molding dies and disused resin of the products are removed; and a part xe2x80x9cFxe2x80x9d is an accommodating section for accommodating the molded products.
As described above, the resin molding machine using the release film has some advantages. For example, the molded products can be easily ejected from the molding die, and the structures of the molding dies can be simpler. The structure of the resin molding machine using the release film is quite different from that of the resin molding machine using no release film. To execute the method of resin molding with the release film, the old molding machines must be fully replaced, so the equipment cost must be quite higher.
However, quality of the molded products, which are molded by the resin molding machine shown in FIGS. 31 and 32, is not fully satisfied. In the case of molding lead frames with resin, the resin molding machine has the following disadvantages: resin flash is apt to be formed on the surface of the molded product; thickness of the molded products are not fixed; and it is difficult to mold thinner products.
In FIGS. 33-35, a work piece (a lead frame of transistors) 200 having heat sinks 202 are molded with resin. The work piece is clamped by molding dies and molded by filling the resin in cavities 206 via gates 204. Dam blocks 208 fill spaces between adjacent work piece 200 so as not to leak the resin. The height of the dam blocks 208 is slightly lower than the thickness of the work piece 200 so as not to damage the opposite parting face of the molding die when the molding dies clamp the work piece 200. Thus, thin resin flash is formed between the dam blocks 208 and the opposite parting face.
The resin flash 210 is formed between the dam block 208 and the work piece 200 and on outer faces of the heat sinks 202. The resin flash 210 is also formed in the peripheral of resin paths connecting pots to the cavities 206, e.g., the gates 204, and in the peripheral of culls 212. This is because securely clamping the work piece 200 has priority over preventing the resin flash, so the resin flash 210 is apt to be formed between the molding dies.
In FIG. 36, a work piece (a plastic circuit board of BGA) 200 is molded with resin. The resin flash 210 is formed in the vicinity of molded parts 214. The thickness of the plastic circuit boards is not fixed, so all plastic circuit boards cannot be clamped with fixed clamping force. Therefore resin flash maybe formed on surfaces of the molded products.
If the molded products have resin flash formed thereon, the step of removing the resin flash is required after a molding step. Furthermore, the resin flash is scattered in all directions when the molded products are taken out from the molding die; the scattered resin causes troubles. Further, if the resin flash is formed on a surfaces of an electric terminal, the molded product cannot be electrically connected.
An object of the present invention is to provide a method of resin molding and a molding machine, which are capable of preventing molded products from forming resin flash on their surfaces.
To achieve the object, the method of the present invention comprises the steps of:
covering over a parting face, which includes a molding section, of at least one of molding dies with release film;
clamping a work piece, with the release film, by the molding dies; and
filling the melted resin in the molding section of the molding die,
wherein the release film is tightly pressed on a surface of a part of the work piece, which is exposed after molding, in the clamping step.
By pressing the release film on the surface of the part of the work piece, the release film prevents the melted resin from invading into a gap between the release film and the work piece, so that no resin flash is formed on the surface of the work piece.
In the method, the part of the work piece, which is exposed after molding, may be located in the molding section of the molding die when the molding dies clamp the work piece.
In the method, the part of the work piece, which is exposed after molding, may be located outside of the molding section of the molding die when the molding dies clamp the work piece.
In the method, the molding section may be formed in the parting face of one of the molding dies, wherein a parting face of the other molding die is a flat face on which the release film is fed.
In the method, an escaping section, in which the release film can be accommodated, may be formed in the parting face of the molding die, whereby deformation of the work piece is prevented when the molding die presses the release film on the surface of the work piece.
In the method, the part of the work piece, which is exposed after molding, may be an electric terminal.
In the method, the part of the work piece, which is exposed after molding, may be a heat radiating part.
In the method, the part of the work piece, which is exposed after molding, may be an optical transparent part.
Furthermore, the resin molding machine of the present invention comprises:
a press section including a couple of molding dies for clamping and molding a work piece to be molded, and a couple of platens to which the molding dies are respectively attached;
a loading section for setting the work piece and a resin material into the molding die of the press section;
an unloading section for conveying a molded product from the press section;
an accommodating section for accommodating the molded product, in which disused resin has been removed;
a film feeding mechanism being provided to one of the platens, the film feeding mechanism feeding release film to cover over a parting face, which includes a molding section, of at least one of the molding dies; and
an air sucking mechanism for fixing the release film on the parting face of the molding die by air suction.
The release film is fed onto the parting face of the molding die by the film feeding mechanism, and the molding section therein is covered with the release film. By the release film, the work piece can be molded without sticking the resin on the molding section.
In the resin molding machine, the loading section may be located on one side of the press section, the unloading section may be located on the other side thereof, and
the film feeding mechanism may feed the release film in the direction perpendicular to a line connecting the loading section and the unloading section.
In the resin molding machine, the film feeding mechanism may comprise:
a feeding roller on which long new release film has been wound, the feeding roller being provided on one side of the molding dies;
a collecting roller for winding used release film, which has passed over the parting face of the molding die, the collecting roller being provided on the other side of the molding dies; and
a driving section for rotating the feeding roller and the collecting roller according to molding action of the resin molding machine.
In the resin molding machine, the width of the release film may be designed to cover over the whole parting face of the molding die.
In the resin molding machine, the width of the release film may be equal to that of the work piece, and
the release film may be fed to a position corresponding to the work piece.
The resin molding machine may further comprise lock blocks being respectively provided to the molding dies and capable of engaging with each other to correctly position the molding dies when the molding dies clamp the work piece, the lock blocks being arranged not to interfere with the release film covering the molding die.
In the resin molding machine, an escaping section, in which the release film can be accommodated, may be formed in the parting face of the molding die.
In the resin molding machine, a drawing groove, into which a slackened part of the release film is drawn by air suction, may be formed in a peripheral of the molding section of the molding die.
In the resin molding machine, a drawing groove, into which a slackened part of the release film is drawn by air suction, may be formed in a peripheral of the escaping section of the molding die.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.